The tag can be used to retrieve the page with [adw.navigation_view.NavigationView.findPage], as well as with [adw.navigation_view.NavigationView.pushByTag], [adw.navigation_view.NavigationView.popToTag] or [adw.navigation_view.NavigationView.replaceWithTags].
Tags must be unique within each class@NavigationView.
The tag also must be set to use the navigation.push action.